Generally, retort food is prepared by mixing unsterilized food materials, such as solid matter and liquid matter, putting in a bag or the like of plastics or aluminum, sealing, applying in a retort apparatus, and heating and processing to sterilize.
In the conventional sterilizing method, since solid matter and liquid matter are heated and processed simultaneously by passing through a sealed bag or the like, processing suited to solid matter and processing suited to liquid matter cannot be done separately, and the processing time tends to be long, ranging from scores of minutes to several hours, and it took a longer time when the thickness of the bag was larger. Accordingly, the food was exposed to high temperature for a long time, which led to problems of deterioration of quality and decline of flavor.
Moreover, when sterilizing solid matter only, hitherto, a large volume was put in a large pressure vessel to sterilize for a long time, and uneven processing and overcooking were likely to occur, or it required weighing or dispensing to distribute into bags after processing, which was often accompanied by deformation, and yet drip or juice exuding from the solid matter at the time of sterilization process remained in the bottom of the pressure vessel, and it was extremely difficult to put it into the bag together with the solid matter, and the drip containing taste components was discarded as waste liquid.